/Engine/Plugins/Experimental/MeshModelingToolsetExp/Source/ModelingEditorUI/Public/ModelingWidgets/ModelingCustomizationUtil.h
Create an error-string widget and add it to the Slot argument, to give the (developer) feedback about slate programming errors
namespace UE { namespace ModelingUI { template<typename SlotType> void UE::ModelingUI::SetCustomWidgetErrorString ( [FText](API\Runtime\Core\Internationalization\FText) ErrorString, SlotType & Slot ) } }